As airline fuel costs and safety concerns and regulations have increased, use of the aircraft main engines is no longer the best option for achieving, the desired safe and efficient ground movement. Various alternatives to the use of an aircraft's main engines to move an aircraft on the ground have been proposed and tried. The use of a tug or tow vehicle to move an aircraft into and out of a gate or parking location can eliminate the need to use the aircraft main engines. This option, however, is not without its own challenges and costs. More ground vehicles, requiring more fuel and more ground personnel to operate them, add to an already congested environment in the gate area. Restricted use of the aircraft engines on low power during arrival at or departure from a gate is an additional option. This option is also problematic, however. Not only does engine use consume fuel, it is also noisy, and the associated safety hazards of jet blast and engine ingestion in a congested area are significant concerns that cannot be overlooked.
The use of a motor structure integrally mounted with a wheel to rotate the wheel and drive a vehicle, including an aircraft, has also been proposed. The use of such a structure, ideally, should move an aircraft with minimal or no use of an aircraft's main engines. U.S. Pat. No. 2,430,163 to Dever and U.S. Pat. No. 3,977,631 to Jenny, for example, describe drive motors associated with aircraft gear wheels intended to drive an aircraft on the ground. The motor assembly disclosed by Jenny includes a reduction gear assembly positioned to facilitate mounting of a drive motor away from the cramped wheel and brake assembly. In U.S. Pat. No. 7,445,178, McCoskey et al describe a powered nose aircraft wheel system with a multifunctional wheel motor coupled to the wheel axle and the wheel. The motor, which may be driven by a planetary gear assembly or by a direct drive, is located within the hub of the wheel, and the wheels are free to spin on an axle strut by rim bearings. U.S. Pat. No. 7,226,018 to Sullivan also describes a wheel hub motor/generator useful in an aircraft landing gear wheel that includes an arrangement of alternating rotor and stator disks designed to provide motive force to an aircraft wheel when electric power is applied. U.S. Pat. No. 7,469,858 to Edelson, owned in common with the present invention, describes a geared wheel motor design that may be used to move an aircraft from a stationary position for taxiing.
Published United States patent applications, including U.S. Patent Application Publication Nos. US2006/0273686 to Edelson, US2007/0282491 to Cox et al, US2009/0261197 to Cox, International Patent Application Publication No. WO 2008/027458 to Cox et al, and British Patent No. 2457144, also owned in common with the present invention, describe aircraft drive systems that use electric drive motors to power aircraft wheels and move an aircraft on the ground. These disclosures focus on specific, aspects of the drive systems and motor assemblies, including drive system data, motor design, and tire profile.
While the wheel motor designs described above may be effectively employed to drive aircraft wheels and, therefore, move aircraft on the ground, none of them specifically addresses the challenges that can arise from the build up of heat in the wheel motor structures. Heat can build up in the wheel motor, primarily from the application of brakes during landing and taxi, but also from the operation of the motor itself. It is widely recognized that motor output decreases as the motor temperature increases. Shielding an aircraft wheel from heat and managing the heat generated by the aircraft brakes and other sources is critical to continued effective functioning of the aircraft wheel. Brake heat can be specifically problematic, moreover, because heat from this source builds up very rapidly and can subject any adjacent wheel or other structures to thermal spikes that can unacceptably weaken these structures. Aircraft wheels are typically made of a forged aluminum alloy that cannot tolerate high temperatures without the subsequent tempering and/or weakening of the wheel material. The known technique of providing a thermal shield to protect an aircraft wheel from the motor-generated and other heat to prevent harm to the wheel may be effective, but this can add undesirable structure and weight to a landing gear assembly.
U.S. Patent Application Publication No. 2009/0152055 to Cox describes means for cooling the brakes in aircraft undercarriage wheels by disengaging and spinning the motor used to provide traction on landing. The spinning of the motor and also the rotor component of the motor produces cooling as air is carried from a cooler location, preferably through holes or tunnels, to the location of the brakes. While this arrangement may effectively provide the requisite cooling during braking, it does not address longer term heat management considerations.
Arrangements for cooling wheel motors have been proposed in the prior art. Sakuma et al, in U.S. Patent Application Publication No. US2009/0236158, disclose a cooling apparatus for an in-wheel electric motor for a vehicle that includes a knuckle structure holding the wheel that functions as a radiator. A supply of a refrigerant, identified as oil, a refrigerant pump, and supply lines are required for operation of the apparatus. This design, while effective for cooling road vehicles, would add additional unacceptable weight and size to an aircraft drive wheel. In U.S. Patent Application Publication No. US2010/0065355, Reddy describes a cooling system for an electric drive motor that uses temperature sensors and electronic controllers to generate and regulate air flow driven by an electric fan and is designed to cool, in conjunction with an internal combustion engine, the wheel motors in large, heavy off-highway vehicles. Not only would this design add additional unacceptable weight if used in an aircraft, but Reddy does not suggest that it could function without the engine. U.S. Patent Application Publication No. US2010/0072837 to Telakowski describes a motor cooling system useful for aircraft moving at low speeds that is intended to maintain the motor at desired operating temperatures during various travel states. Cooling fluid is received from ram air and a secondary source, such as an aircraft compartment, in response to the aircraft operating state. There is no suggestion, however, that this system could be used in drive wheel motors or motors other than the fan and compressor motors described therein.
The prior art, therefore, does not suggest apparatus or method designed to effectively manage heat in an in-wheel motor suitable for use in an aircraft ef or other vehicle drive wheel that does not add unacceptable bulk or additional components to the wheel structures or wheel well or that effectively uses a wheel structure to direct heat flow away from the aircraft. None of the foregoing patents or publications, moreover, suggests heat management in an aircraft wheel that is specifically configured to maximize the limited landing gear space available by integrating within the wheel a compact motor and gear assembly capable of powering an aircraft drive wheel. This art, moreover, does not contemplate a wheel structure shaped for optimum heat management to support an integral configuration of wheel, heat management structure, motor, and gear components that can be retrofitted in existing aircraft or that provides easy access to these components for maintenance and repair when the motor is not in operation.
A need exists, therefore, for effective heat management in an in-wheel motor suitable for use in an aircraft drive wheel or other vehicle wheel used to move the aircraft or other vehicle that employs the wheel in a heat conduction pathway that allows heat to be shed entirely away from the aircraft. A need also exists for heat management in an aircraft wheel that is specifically configured to maximize, the limited landing gear space available by integrating within the wheel a compact motor and gear assembly capable of powering an aircraft drive wheel that can be installed in an existing aircraft without modification of landing gear structures.